In thirty years of a multi dog pack, that hasn't been my experience. Oh I had brothers that fought, that was costly. And once the girls got into it, punctures mostly. And then Huey - the Bullchit, went after Nicky the Pit Bull, but the Pit was good natured and called off. A dog can run into a tree in the yard and die, I've known two people with dogs who killed themselves that way. Known a bunch with dogs who choked/impacted from eating things they shouldn't - like rocks.
I did know a guy who was warned NOT to buy two male rotts, siblings, he did it anyway, when they finally decided to have it out, he was in the middle and they BROKE his arms, both of them, then near killed one another.
Yes TRUST kills at times, trust not to kill each other, trust not to run into trees, trust not to eat rocks, trusted off leash even... But that's life, and dogs and living things. And my packs love each other, obviously depend on each other, 9 at a time in the yard, do not pack up on one another automatically, nor three or more. And people who DO NOT know their dogs well, and cannot tell when there are disagreements about to happen, and don't see dominance symptoms and respond properly DO lose dogs. If I'd kept Nicky and Huey together after that last fight, I know Huey would attack him again, and Nicky would FINISH it. So I placed the dog, he's quite happy with his five kids and cat.
Absolutely any two dogs can decide to kill one another at any time, at any point in their lives. Absolutely packs can decide to go after one pack member and kill them. Little dogs or large. Or a dog can choke, hang itself, impact from eating things. Suddenly and for the first time run off and into traffic and die. I could spend my whole waking life trying to keep them safe from life. Nah. I'm aware and watchful and I know them. They matter to one another, it's obvious, and after 30 years this way, I'd go down to four but no fewer, and I've run up to 15 successfully for years.
Pack animals are pack animals and I prefer to do it that way, risks acknowledged.
Cher